Effect of Gravity and Noncondensable Gas Levels on Condensation in Variable Conductance Heat Pipe

An experimental and analytical study was conducted to examine the flowfield behavior of a vapor-noncondensable gas mixture and its effect on heat transfer rate in the condenser of a variable conductance heat pipe (VCHP) or thermosyphon. Detailed temperature distributions and heat transfer rate were measured, and a flowfield visualization was made using a laser holographic interferometer. In order to investigate the dominant physical parameters in the flowfield, a numerical simulation was performed. It was found that the gravity force and levels of noncondensable gas contained have a strong effect on the location and the profile of an interfacial layer. The proposal of the formation of a clear diffusion front layer in the condenser would lead to an erroneous interpretation of thermofluid dynamic behavior of VCHPs for terrestrial use or ground-based testing.